How quickly do premature babies grow?

Our lovely Zaki was due on 12 February 2018, but my waters broke on 11 January and he popped out on 12th January 2018 - a calendar month early!

We were all worried that he was healthy, as there are so many stats and complications of being born early.  The guidance states that premature babies' weights should be tracked against their corrected age,  which is the chronological age minus weeks born premature, on standard term growth charts. 

Well, how did Zaki do? Here is his weight for the first month, until 15 February, against a backdrop of the WHO percentiles for expected growth. 

Wow, Zaki! A month after he was born, he had increased his weight by more than 50%! This chart is for chronological age, NOT corrected age. 

So should we be using corrected age, or chornological age? Well, we can compare to Oren, Zaki's older brother. 

By day 50, Zaki was already approaching Oren's trajectory. They are remarkably similar by 150 days chronological age: 

Zaki's on the chronological trajectory from about day 50. By 70 days he had more than doubled his birth weight. The key difference in growth between them was in the first 30 days. Around 2 weeks old, Zaki was gaining an average of 70g a day.